Maximum power point tracking controllers and associated systems and methods

• US 9,141,123 B2
• Filed: 10/16/2012
• Issued: 09/22/2015
• Est. Priority Date: 10/16/2012
• Status: Active Grant

• Current Assignee: Volterra Semiconductor Corporation (Analog Devices, Inc.)
• Original Assignee: Volterra Semiconductor LLC (Analog Devices, Inc.)
• Inventors: McJimsey, Michael D., Stratakos, Anthony J., Jergovic, Ilija, Zhang, Xin, Yao, Kaiwei, Ng, Vincent W., Nguyen, Phong T., Minassians, Artin Der
• Primary Examiner(s): Tran, Nguyen
• Application Number:
  US13/653,381
• Publication Number:
  US 20140103894A1
• Time in Patent Office: 1,071 Days
• Field of Search: 323/207, 323/222, 323/271, 323282-285
• US Class Current: 1/1
• CPC Class Codes: G01R 21/06 by measuring current and voltage G01R21/08 - G01R21/133 take precedence
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: H03K 3/356165 using additional transistors in the feedback circuit
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A maximum power point tracking controller includes an input port for electrically coupling to an electric power source, an output port for electrically coupling to a load, a control switching device, and a control subsystem. The control switching device is adapted to repeatedly switch between its conductive and non-conductive states to transfer power from the input port to the output port. The control subsystem is adapted to control switching of the control switching device to regulate a voltage across the input port, based at least in part on a signal representing current flowing out of the output port, to maximize a signal representing power out of the output port.

Claims

1. A maximum power point tracking controller, comprising:

an input port for electrically coupling to an electric power source;

an output port for electrically coupling to a load;

a control switching device adapted to repeatedly switch between conductive and non-conductive states to transfer power from the input port to the output port; and

a control subsystem adapted to control switching of the control switching device to regulate a voltage across the input port, based at least in part on a signal representing current flowing out of the output port, to maximize a signal representing power out of the output port;

the control subsystem further adapted to;

control switching of the control switching device based partially on the signal representing current flowing out of the output port and a difference between the voltage across the input port and a reference voltage,

vary a magnitude of the reference voltage to maximize the signal representing power out of the output port, and

control switching of the control switching device based partially on an error signal given by −

Kv*(Vin−

Vref)+Ki*Io, where Kv is a first scaling factor, Ki is a second scaling factor, Vin is the voltage across the input port, Vref is the reference voltage, and Io is the signal representing current flowing out of the output port.

2. The maximum power point tracking controller of claim 1, the control switching device being electrically coupled between a first terminal of the input port and a first terminal of the output port, the maximum power point tracking controller further comprising a freewheeling device electrically coupled between the first terminal of the output port and a second terminal of the output port, the freewheeling device adapted to provide a path for current flowing between the first and second terminals of the output port when the control switching device is in its non-conductive state.

3. The maximum power point tracking controller of claim 2, the control subsystem comprising a multiplier adapted to determine the signal representing power out of the output port from a product of a scaled signal representing average voltage across the output port and a scaled signal representing average current flowing out of the output port.

4. The maximum power point tracking controller of claim 3, the control subsystem further comprising:

a voltage scaling subsystem adapted to generate the scaled signal representing average voltage across the output port by scaling a signal representing average voltage across the output power-port to be within a first predetermined range; and

a current scaling subsystem adapted to generate the scaled signal representing average current flowing out of the output port by scaling a signal representing average current flowing out the output port to be within a second predetermined range.

5. The maximum power point tracking controller of claim 4, the current scaling subsystem further adapted to prevent a magnitude of the scaled signal representing average current flowing out of the output port from falling below a minimum threshold value.

6. The maximum power point tracking controller of claim 5, the current scaling subsystem further adapted to add a positive offset value to the scaled signal representing average current flowing out of the output port when the signal representing average current flowing out the output port is within a first range of values.

7. The maximum power point tracking controller of claim 4, the control subsystem further comprising a current filter subsystem adapted to generate the signal representing average current flowing out of the output port by filtering the signal representing current flowing out the output port.

8. The maximum power point tracking controller of claim 7, the control subsystem further comprising a voltage filter subsystem adapted to generate the signal representing average voltage across the output port by filtering a signal representing voltage across the output port.

9. The maximum power point tracking controller of claim 1, the control subsystem further adapted to inhibit a reduction in the magnitude of the reference voltage when the voltage across the input port falls below a threshold value.

10. The maximum power point tracking controller of claim 1, the control subsystem further adapted to inhibit a reduction in the magnitude of the reference voltage when doing so would cause the voltage across the input port to fall below a threshold value.

11. The maximum power point tracking controller of claim 1, the control subsystem further adapted to inhibit an increase in the magnitude of the reference voltage when the voltage across the input port rises above a threshold value.

12. The maximum power point tracking controller of claim 1, the control subsystem further adapted to:

change the magnitude of the reference voltage by a first step size, to maximize the signal representing power out of the output port, when a command to control a duty cycle of the control switching device is below a first threshold value; and

change the magnitude of the reference voltage by a second step size, to maximize the signal representing power out of the output port, when a command to control a duty cycle of the control switching device is greater than or equal to a second threshold value;

the second step size being smaller than the first step size.

13. The maximum power point tracking controller of claim 12, the first threshold value being the same as the second threshold value.

14. The maximum power point tracking controller of claim 1, the control subsystem further adapted to:

change the magnitude of the reference voltage by a first step size, to maximize the signal representing power out of the output port, when a difference in the signal representing power out of the output port between successive changes in magnitude of the reference voltage is below a first threshold value; and

change the magnitude of the reference voltage by a second step size, to maximize the signal representing power out of the output port, when a difference in the signal representing power out of the output port between successive changes in magnitude of the reference voltage is greater than or equal to a second threshold value;

the second step size being greater than the first step size.

15. The maximum power point tracking controller of claim 14, the first threshold value being the same as the second threshold value.

16. The maximum power point tracking controller of claim 1, the control subsystem further adapted to:

change the magnitude of the reference voltage at a first rate, to maximize the signal representing power out of the output port, when a command to control a duty cycle of the control switching device is within a first range of values; and

change the magnitude of the reference voltage at a second rate, to maximize the signal representing power out of the output port, when the command to control the duty cycle of the control switching device is within a second range of values;

the second rate being greater than the first rate.

17. The maximum power point tracking controller of claim 16, the first range of values representing a command that the duty cycle of the control switching device be between zero and one hundred percent, and the second range of values representing a command that the duty cycle of the control switching device be less than zero or greater than one hundred percent.

18. The maximum power point tracking controller of claim 1, the control subsystem further adapted to increase the magnitude of the reference voltage in response to the magnitude of the voltage across the input port falling below a threshold value.

19. The maximum power point tracking controller of claim 1, the control subsystem further adapted to set an initial magnitude of the reference voltage based at least partially on an initial value of the voltage across the input port, at start-up of the switching circuit.

20. The maximum power point tracking controller of claim 19, the control subsystem further adapted to set the initial magnitude of the reference voltage to a fraction of the voltage across the input port, at start-up of the switching circuit.

21. The maximum power point tracking controller of claim 1, the control subsystem further adapted to decrease the magnitude of the reference voltage in response to the signal representing current flowing out of the output port indicating that a magnitude of current flowing out of the output port has fallen below a first threshold level.

22. The maximum power point tracking controller of claim 21, the control subsystem further adapted to operate the control switching device at a fixed duty cycle in response to the signal representing current flowing out of the output port indicating that a magnitude of current flowing out of the output port has fallen below a second threshold level, where the second threshold level is lower than the first threshold level.

23. The maximum power point tracking controller of claim 1, the control switching device and the control subsystem being part of a common integrated circuit.

24. The maximum power point tracking controller of claim 1, wherein:

the control switching device comprises a dynamically sized field effect transistor;

the maximum power point tracking controller further comprises a current reconstructor subsystem adapted to generate the signal representing current flowing out of the output port, the current reconstructor subsystem having a gain at least partially dependent on a size of the dynamically sized field effect transistor; and

the control subsystem is adapted to decrease a size of the dynamically sized field effect transistor if a magnitude of the signal representing current flowing out of the output port falls below a threshold value, thereby increasing the gain of the current reconstructor subsystem.

25. An electric power system, comprising:

an electric power source; and

a maximum power point tracking controller, including;

an input port electrically coupled to the electric power source,

an output port for electrically coupling to a load,

a control switching device adapted to repeatedly switch between conductive and non-conductive states to transfer power from the electric power source to the output port, and

a control subsystem adapted to control switching of the control switching device to regulate a voltage across the input port, based at least in part on a signal representing current flowing out of the output port, to maximize a signal representing power out of the output port;

the control subsystem further adapted to;

control switching of the control switching device based partially on the signal representing current flowing out of the output port and a difference between the voltage across the input port and a reference voltage,

vary a magnitude of the reference voltage to maximize the signal representing power out of the output port, and

control switching of the control switching device based partially on an error signal given by −

Kv*(Vin−

Vref)+Ki*Io, where Kv is a first scaling factor, Ki is a second scaling factor, Vin is the voltage across the input port, Vref is the reference voltage, and To is the signal representing current flowing out of the output port.

26. The electric power system of claim 25, the electric power source comprising a photovoltaic device.

27. The electric power system of claim 26, the photovoltaic device comprising a plurality of interconnected photovoltaic cells.

28. The electric power system of claim 26, the photovoltaic device comprising a multi-junction photovoltaic cell.

29. The electric power system of claim 25, the control switching device being electrically coupled between a first terminal of the input port and a first terminal of the output port, the maximum power point tracking controller further comprising a freewheeling device electrically coupled between the first terminal of the output port and a second terminal of the output port, the freewheeling device adapted to provide a path for current flowing between the first and second terminals of the output port when the control switching device is in its non-conductive state.

30. The electric power system of claim 29, the control subsystem comprising a multiplier adapted to determine the signal representing power out of the output port from a product of a scaled signal representing average voltage across the output port and a scaled signal representing average current flowing out of the output port.

31. The electric power system of claim 30, the control subsystem further adapted to prevent a magnitude of the scaled signal representing average current flowing out of the output port from falling below a minimum threshold value.

32. The electric power system of claim 26, the control switching device and the control subsystem being part of a common integrated circuit.

33. The electric power system of claim 32, the common integrated circuit and the photovoltaic device being co-packaged.

34. The electric power system of claim 25, further comprising one or more additional maximum power point tracking controllers electrically coupled in series with the output port and the load, each additional maximum power point tracking controller adapted to transfer power from a respective additional electric power source to the load.

35. A method for operating a maximum power point tracking controller including an input port for electrically coupled to an electric power source and an output port for electrically coupling to a load, comprising the steps of:

repeatedly switching a control switching device of the maximum power point tracking controller between conductive and non-conductive states to transfer power from the input port to the output port;

controlling switching of the control switching device, based at least in part on a signal representing current flowing out of the output port, to regulate a magnitude of a voltage across the input port such that a signal representing power out of the output port is maximized;

controlling switching of the control switching device partially based on the signal representing current flowing out of the output port and a difference between the magnitude of the voltage across the input port and a reference voltage;

varying a magnitude of the reference voltage to maximize the signal representing power out of the output port; and

controlling switching of the control switching device partially based on an error signal given by −

Kv*(Vin−

Vref)+Ki*Io, where Kv is a first scaling factor, Ki is a second scaling factor, Vin is the voltage across the input port, Vref is the reference voltage, and Io is the signal representing current flowing out of the output port.

36. The method of claim 35, further comprising determining the signal representing power out of the output port by multiplying a signal representing average voltage across the output port by a signal representing average current flowing out of the output port, using a multiplier.

37. The method of claim 36, further comprising filtering the signal representing current flowing out of the output port to generate the signal representing average current flowing out of the output port.

38. The method of claim 37, further comprising filtering a signal representing voltage across the output port to generate the signal representing average voltage across the output power port.

39. The method of claim 38, further comprising preventing a magnitude of the signal representing average current flowing out of the output port from falling below a minimum threshold value.

40. The method of claim 35, further comprising:

storing a first sample of the signal representing power out of the output port when a duty cycle of the control switching device is one hundred percent duty cycle;

decreasing the magnitude of the reference voltage by a first amount;

storing a second sample of the signal representing power out of the output port, after the step of decreasing the magnitude of the reference voltage by the first amount;

comparing the first sample of the signal representing power out of the output port to the second sample of the signal representing power out of the output port;

increasing the magnitude of the reference voltage when the first sample of the signal representing power out of the output port is greater than the second sample of the signal representing power out of the output port; and

decreasing the magnitude of the reference voltage when the second sample of the signal representing power out of the output port is greater than the first sample of the signal representing power out of the output port.

41. The method of claim 35, further comprising inhibiting a reduction in the magnitude of the reference voltage when the voltage across the input port falls below a threshold value.

42. The method of claim 35, further comprising inhibiting an increase in the magnitude of the reference voltage when the voltage across the input port rises above a threshold value.

43. The method of claim 35, further comprising:

changing the magnitude of the reference voltage by a first step size, to maximize the signal representing power out of the output port, when a command to control a duty cycle of the control switching device is below a first threshold value; and

changing the magnitude of the reference voltage by a second step size, to maximize the signal representing power out of the output port, when a command to control a duty cycle of the control switching device is greater than or equal to a second threshold value;

the second step size being smaller than the first step size.

44. The method of claim 35, further comprising:

changing the magnitude of the reference voltage at a first rate, to maximize the signal representing power out of the output port, when a command to control a duty cycle of the control switching device is within a first range of values; and

changing the magnitude of the reference voltage at a second rate, to maximize the signal representing power out of the output port, when the command to control the duty cycle of the control switching device is within a second range of values;

the second rate being greater than the first rate.

45. The method of claim 44, the first range of values representing that the duty cycle of the control switching device is commanded to be between zero and one hundred percent, and the second range of values representing that the duty cycle of the control switching device is commanded to be less than zero or greater than one hundred percent.

46. The method of claim 35, further comprising increasing the magnitude of the reference voltage in response to the magnitude of the voltage across the input port falling below a threshold value.

47. The method of claim 35, further comprising setting an initial magnitude of the reference voltage based at least partially on an initial value of the voltage across the input port, at start-up of the switching circuit.

48. The method of claim 47, further comprising setting the initial magnitude of the reference voltage to a fraction of the voltage across the input port, at start-up of the switching circuit.

49. The method of claim 35, further comprising decreasing the magnitude of the reference voltage in response to a magnitude of current flowing out of the output port falling below a first threshold level.

50. The method of claim 49, further comprising operating the control switching device at a fixed duty cycle in response to a magnitude of current flowing out of the output port falling below a second threshold level, where the second threshold level is lower than the first threshold level.

51. The method of claim 35, further comprising:

generating the signal representing current flowing out of the output port using a current reconstructor subsystem; and

decreasing a size of a dynamically sized field effect transistor of the control switching device when a magnitude of the signal representing current flowing out of the output port falls below a threshold value, thereby increasing a gain of the current reconstructor subsystem.